Module 3 Section 1: Exchange and Transport Flashcards
Substance exchange in cells
Cells need to take in things like oxygen and glucose for metabolic reactions
They need to excrete waste products from these reactions like carbon dioxide and urea
What decides the difficulty at which substances can be exchanged in cells
The surface area : volume ratio
How to find SA : V ratio of cuboid 4 x 4 x 2
Volume: 2 x 4 x 4 = 32cm3
Surface area: 2 x 4 x 4 = 32cm2 ( top and bottom surfaces )
+ 4 x 2 x 4 ( four sides of the cube )
Why do multicellular organisms need exchange surfaces
In multicellular animals, diffusion across the outer membrane is too slow because:
Some cells are deep inside the body - there’s a big distance between them and the outside environment
Large animals have a low surface area to volume ratio - its difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface
Multicellular organisms have a higher metabolic rate than single celled organisms, so they use up oxygen and glucose faster
why don’t single celled organisms need exchange surfaces
In single celled organism, these substances can diffuse directly in or out of the cell across the cell surface membrane.
The diffusion rate is quick because of the small distances the substances have to travel
How are root hair cells adapted for exchange of substances
Large surface area:
Cells on plant roots grown into long hairs which stick into the soil, each root branch will have millions of thee hairs
This gives the roots a large surface area which helps increase the absorption of water by osmosis and mineral ions by active transport
How are alveoli adapted for exchange of substances
Short diffusion pathway:
Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium
O2 diffuses out of the alveolar space into the blood, CO2 diffuses out
The thin alveolar epithelium helps to decrease the distance over which O2 ad XCO2 diffusion takes place and increases the rate of diffusion
Good blood supply:
surrounded by large capillary, giving each alveolus has its own blood supply. blood constantly takes oxygen away and bring carbon dioxide to the alveoli
Good ventilation:
Lung ventilated so air in each alveolus is constantly replaced
Features of exchange surfaces to improve efficiency
Large surface area
Thin
Good blood supply or ventilation
How are fish gills adapted for substance exchange
Large surface area
Good blood supply:
Large network of capillaries which keeps them well supplied with blood
Well ventilated:
Fresh water constantly passes over them
This maintains the concentration gradient of O2 which increase the rate at which O2 diffuses into the blood
Structure of the lungs
As you breathe in, air enters the trachea
Trachea splits into two bronchi - one bronchus leading to each lung
Each bronchus then branches off into smaller tubes called bronchioles
Bronchioles end in small sacs called alveoli where gas is exchanged
Ribcage, intercostal muscles’ and diaphragm all work together to bring air in and out
Function of goblet cells
Secrete mucus
The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli
Function of the cilia
Cilia ( on the surface of cells lining airways ) beat mucus
this moves the mucus upward away from the alveoli towards the throat where it is swallowed
Function of elastic fibres
Elastic fibres in walls of the trachea, bronchi, bronchioles and alveoli help process of breathing out
On breathing in, the lungs inflate and the fibres are stretched, then recoil to push air out during exhalation
Function of smooth muscle
Smooth muscles in trachea walls, bronchi and bronchioles allows their diameter to be controlled
Smooth muscle relaxes during exercise and makes tubes wider
Creates less resistance to airflow and air can move in and out of lungs more easily
Function of rings of cartilage
Rings of cartilage in wall of the trachea and bronchi
Provide support
Strong and flexible to stop trachea and bronchi collapsing when you breathe in and pressure drops
Structure of trachea
Large C shaped rings of cartilage
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium
Structure of Bronchi
Smaller rings of cartilage
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium
Structure of larger, smaller and smallest bronchioles
Larger:
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium
Smaller:
Smooth muscle
Elastic fibres
Ciliated epithelium
Smallest:
Smooth muscle
Elastic fibres
Ciliated epithelium
Structure of alveoli
No cartilage
Smooth muscle
Elastic fibres
Regular epithelium ( no cilia )
Process of Inspiration
The external intercostal and diaphragm muscles contract
This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax
As the volume of the thorax increases, the lung pressure decreases to below atmospheric pressure
This causes air to flown into the lungs
Inspiration is an active process - it requires energy
Process of expiration
The external intercostal and diaphragm muscles relax
The ribcage moves downwards and inwards and the diaphragm becomes curved again
The thorax volume decreases, causing the air pressure to increase to above atmospheric pressure
Air is forced out of the lungs
Normal expiration is a passive process - it doesn’t require energy
Expiration can be forced ( e.g. blowing or sighing ), this is when the internal intercostal muscles contract to pull the ribcage down and in
What does tidal volume mean
The volume of air in each breath - usually about 0.4dm3
What does vital capacity mean
The maximum volume of air that can be breathed in or out
What does breathing rate mean
How many breaths are taken - usually in a minute
What does oxygen consumption or oxygen uptake mean
The rate at which an organism uses up oxygen ( e.g. the number of dm3 used per minute )
How can a spirometer be used to investigate breathing
A spirometer has an oxygen filled chamber with a movable lid
The person breathes through a tube connected to the oxygen chamber
As the person breathes in and out, the lid of the chamber moves up and down
These movements can be recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace. Or the spirometer can be hooked up to a motion sensor - this will use the movements to produce electronic signals, which are picked up by a data logger
The soda lime in the tube the subject breathes into absorbs carbon dioxide
What happens when a fish opens it’s mouth
The fish opens its mouth, which lowers the floors of the buccal cavity ( the space inside the mouth )
The volume of the buccal cavity increases which decreases the pressure inside the cavity.
Water is then sucked into the cavity
What happens when a fish closes it’s mouth
When the fish closes it’s mouth, the floor of the buccal cavity is raised again
The volume inside the cavity decreases, the pressure increases, water is forced out of the cavity across the gill filaments
Each gill covered by a bony flap called the operculum ( which protects the gill )
The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills
Structure of a fish’s gas exchange system
Water containing oxygen, enters the fish through its mouth and passes out through the gills
Each gill is made of lots of thin branches called gill filaments or primary lamellae, which provide a large surface area for exchange of gases
The gill filaments are covered in lots of tiny structures called gill plates or secondary lamellae, which increase the surface area even more
Each gill is supported by a gill arch
How do fish use a counter-current system for gas exchange
Blood flows through the gill plates in one direction and water flows over in the opposite direction
This is called a counter current system
It maintains a large concentration gradient between the water and the blood
The concentration of oxygen in the water is always higher than that in the blood
So as much oxygen as possible diffuses from the water into the blood
Always a preferential conc gradient
How does the gas exchange system work in insects
Insects have microscopic air-filled pipes called tracheae which they use for gas exchange
Air moves into the tracheae through pores on the insect’s surface called spiracles
Oxygen travels down the concentration gradient towards the cells
Carbon Dioxide moves down its own concentration gradient towards the spiracles to be released into the atmosphere
The tracheae branch off into smaller tracheoles which have thin permeable wall and go to individual cells
The tracheoles also contain fluid, which oxygen dissolves in
Insects use rhythmic abdominal movements to change the volume of their bodies and move air in and out of the spiracles
When larger insects are flying, they use their wing movements to pump their thoraxes
Why is a concurrent exchange system worse than a countercurrent
Blood flows parallel to water flowing over the gills
Initially there is a very steep concentration gradient
As oxygen poor blood passes the oxygen rich water
However, an equilibrium is reached and diffusion then stops
How do insects maintain aerobic respiration in increasingly anaerobic conditions
Anaerobic respiration leads to build up of lactic acid in the muscle tissues
As a result, water is drawn out of the tracheoles by osmosis ( lower water potential in cells )
Reduces volume of tracheal fluid in the tracheoles
This exposes more surface area in the tracheoles
Allows more oxygen to be absorbed
How to find oxygen uptake, tidal volume and vital capacity on a spirometer graph
